Method of treating hides, skins, and pelts



Mica Aug. 17, 1943 METHOD OF TREATING HIDES, SKINS,

' AND PELTS Julius Pfannmuiler,

North Plainiield, siznor to Walierstein Company, Inc.,

N. J.. as- New York,

N. Y., a corporation of New York No Drawing. Application February 16, 1939, Serial No. 256,719

9 Claims.

This invention relates to a method of treating hides, skins and pelts.

In the production of leather, various operation are involved including dehairing, hating, pickling and tanning. Under ordinary circumstances the skins, hides or pelts are subjected to a preliminary soaking operation prior to dehairing. This soaking step is of considerable importance. Hides, skins and pelts are normally preserved by salting or drying, pending tannery operations. The main object of the soaking operation is to bring the preserved hides, skins or pelts as nearly as possible back to the soft state characteristic of their condition immediately following slaughtering of the animal and before salting or drying. The attainment of proper results in the soaking operation offers considerable difliculty, particularly in the case of skins, hides and pelts which have been dried. To obtain proper leather, this I preliminary soaking operation should result in a softening that is uniform in degree, with no unsoftened spots or areas. Also, the soaking operation should be so carried out as to avoid or prevent any damage to the hides, skins or pelts by reason of excessive bacterial action. As is known in tannery practice, a prolonged soaking period results in a more thorough and uniform softening. On the other hand, the longer the soaking period the greater the danger of excessive bacterial action that will damage the skins. Long soaking periods are also undesirable for reasons of cost, trouble and the like. While the bacterial action may be retarded by soaking at low temperatures, a longer period is required to obtain proper soaking. While higher temperatures shorten the time required, they enhance the danger of bacterial attack.

Various methods of shortening the soaking period and avoiding the disadvantages and dangers involved in prolonged soaking have been proposed from time to time. Only a few, however, have been put into actual use.

At the present time, the most commonly used method of accelerating the soaking action is to add some alkaline substance such as caustic alkali or alkaline sulphides. But the use of such agents is attended with more or less objectionable results. Hides, skins and pelts take up alkali rapidly and thereby become more or less swollen. This occurs, for example, when skins are subjected to a lime or other alkaline bath for hair loosening. But in order to obtain uniform leather, particularly if the finished leather should show a fine and tight grain, the skins should not be subjected to any alkaline treatment unless they are in a uniformly soft condition. Thus, in the alkaline treatment involved ,in unhairing, this difliculty can be. avoided if the skins'have been previously properly softened by soaking. But the addition of alkaline materials to the soaking bath before the skins are properly and uniformly softened, always entails the danger of an uneven absorption of these substances and consequently irregular behavior through all the subsequent processes, and, finally, variations in variou degrees in the final leather.

It is an object of the present invention to provide a method of treating hides, skins and pelts such that the disadvantages of the above described dilemma in connection with soaking operations are avoided.

More particularly, it is an object of the invention to provide a method of soaking hides, skins and pelts such that a thorough and uniform softening of the same, and at the same time a thorough loosening of the dirt of the skins, is attained without requiring prolonged soaking periods.

Other objects and advantages of the invention will be apparent from the following description.

In carrying out the presentinvention I subject dried or salted skins, hides or pelts to a soaking operation in a dilute aqueous bath containing one or more water-soluble sulphur compounds in which the sulphur is combined with hydrogen or hydrocarbon or substituted hydrocarbon radicals of aromatic or aliphatic origin. The members of this group, in addition to hydrogen sulphide and the hydrogen polysulphides, may be considered as derivatives of hydrogen sulphide or polysulphides by replacement of one or two hydrogens by aliphatic or aromatic radicals or by an amine or ammonia group or an aliphatic or aromatic amine or by replacement of one hydrogen by an alkali metal or alkaline earth metal.

Only relatively small amounts of the materials referred to need be used in the soak bath to obtain the desired results. While the amount may vary, even less than 0.05% of hydrogen sulphide, for example, based on weight of skins, if used in an aqueous solution of about 0.01% hydrogen sulphide produces effective results.

The sulphur compound or compounds need not necessarily be added to the bath as such. They may, if desired, be generated in the bath. Such procedure is particularly convenient when it is desired to use hydrogen sulphide since it avoids the more or less obvious disadvantages of storing and handling HzS gas. In other cases, the starting materials for generating a given compound may be more available or more convenient than the compound itself.

As an example of such generation in the bath, a sulphur compound or compounds of the character above referred to may be obtained by adding a suitable sulphide and an acid or acid salt.

When, for example, sodium sulphide and hydrochloric acid are brought together, two reactions are, or may be involved:

(1) Na:S+HCl- NaCl+NaSH (2) NaSH-i-HCl NaCl+I-I2S In carrying out the invention to what is now considered the best advantage, when such starting materials are used I so proportion the same that there is enough HCl in excess of the requirements of Reaction (1) to transform at least a substantial portion of the NaSH into H25 in accordance with Reaction (2) It is to be understood that other sulphides may be used in generating the desired sulphur compounds in the bath by reactions of the general type above referred to. For example, the sulphides of the alkali-alkaline earth groups, with which is grouped, at least theoretically, ammonium sulphide, may be used. As further examples of acids, boric acid and carbonic acid may be used.

When the sulphur compound to be used is something other than hydrogen sulphide, it may be generated in the bath by a reaction of the type exemplified by the following:

' prisingly rapid soaking action attained but, in

addition, the softening is uniform and thorough, approximating closely the soft state the skins have after slaughtering. The softening action is so rapid its effect can often be observed after even a few minutes and the total soaking period can be reduced to less than half the time normally required. The liquors also become very dirty in a short time, indicating that the dirt of the skins is also removed rapidly.

Moreover, the treatment described in no way interferes with subsequent hair-loosening operations. In fact, I have found that if an alkaline hair-loosening bath is used, the latter operation is improved by the preceding soaking treatment.

If the skins are to be subjected to a lime or other alkaline hair-loosening operation, the hair loosening agents may, if desired, be added di-' rectly to the soak bath after the softening treatment.

The following procedures are given by way of example: Example I Put 100 pounds green salted calfskins in a soakliquor consisting of about 450 pounds of water to which has been added 0.5 pound fused sodium sulphide (approximately 62% NazS) and 1.1 pounds hydrochloric acid (18.2%HC1). pH before addition of skins 6.5. Paddle the skins well and leave overnight. The skins are then ready for the dehairing process.

Example II Wash pounds green salted calfskins for 15 minutes. Transfer to a paddle containing about 500 pounds water. With the skins well submerged, inject a slow stream of hydrogen sulphide (HzS) gas into the water so as to obtain an HzS content of about 0.01%. Paddle well and leave overnight plus a few hours.

Example III Wash 100 pounds green salted calfskins and transfer to a soak liquor consisting of about 450 pounds water to which has been added 0.3 pound of monoethy1 sulphide. Paddle well and leave for 15 hours.

What is claimed is:

1. The method of treating salted or dried skins, hides and pelts for preliminary softening of the same, which comprises subjecting the skins,.

hides or pelts to the action of an aqueous bath containing hydrogen sulphide.

2. The method of treating salted or dried skins, hides and pelts for preliminary softening of the same, which comprises adding to an aqueous bath materials capable of liberating hydrogen sulphide, and subjecting the skins, hides or pelts to the action of such bath.

3. The method of treating salted or dried skins, hides and pelts for preliminary softening of the same, which comprises adding to an aqueous bath a sulphide and an acid showing a greater dis-association in water than H28, and subjecting the skins, hides or pelts to the action of such bath.

4. The method of treating salted or dried skins, hides and pelts for preliminary softening of the same, which comprises adding to an aqueous bath sodium sulphide and hydrochloric acid and subjecting the skins, hides or pelts to the action of such bath.

5. The method of treating salted or dried skins, hides and pelts for preliminary softening of the same, which comprises adding to an aqueous bath a sulphide selected from the group consisting of the alkali-alkaline earth sulphides and hydrochloric acid, the acid being added in suflicient excess of the amount necessary to form sodium sulphydrate, to form a substantal amount of hydrogen sulphide, and subjecting the skins, hides or pelts to the action of such bath.

6. The method of treating salted or dried skins, hides and pelts for preliminary softening of the same, which comprises adding to an aqueous bath a sulphide selected from the group consisting of the alkali-alkaline earth sulphides and a reagent selected from the group consisting of acids and acid salts, said reagent being capacitated and being added in sufficient proportions to cause the formation of a substantial amount of hydrogen sulphide, and subjecting the skins, hides or pelts to the action of such bath.

'7. The method of ,treating salted or dried skins, hides and pelts for preliminary softening of the same, which comprises adding to an aqueous bath a sulphide selected from the group consisting of the alkali-alkaline earth sulphides, and hydrochloric acid, and subjecting the skins, hides or pelts to the action of such bath.

8. The method of treating sal ,ed or dried skins, hides and pelts for preliminary softening of the same, which comprises adding to an aqueous bath a sulphide selected from the group consisting of the alkali-alkaline earth sulphides, and a reagent selected from the group consisting of acids and acid salts, and subjecting the skins, hides or pelts to the action of such bath.

9. The method of treating salted or dried skins, hides and pelts for preliminary softening of the same, which comprises adding to an aqueous bath a sulphide selected from the group consisting of the alkali-alkaline earth sulphides, and an acid selected from the group consisting of hydrochloric, boric and carbonic acids, and subjecting the skins, hides or pelts to the action of such bath.

JULIUS PFANNMULLER. 

